You are talking about a DSLR with "live view".
The original DSLRs did not have live view.
It had an optical viewfinder only.
The mirror only had to duck out of the way when the picture is actually taken.
It did have a LCD, but it was for looking at pictures you had taken previously and for looking at the menu.
Live view is more complicated and is still changing.
They keep finding different ways to do the job.
Here is a write-up:
There is a link at the bottom of that page.
Click that link to read even more.
The question I have is about the LCD view screen in DSLRs. Block diagrams of DSLRs show the mirror and shutter in front of the imaging sensor. Where does the LCD screen get it's picture information since light is not allowed to hit the sensor until the shutter opens and the mirror is out of the way? Is there a second sensor supplying the LCD screen?